Leaf-blotch (causal agent Rhynchosporium)

Kevin King - Nottingham University

Leaf-blotch (causal agent Rhynchosporium) is one of the most important diseases of barley in the UK. This fungal pathogen causes lesions, with pale centres and tan-margins (Fig. 1), on leaves which can reduce yields by up to 40%. One potential source of inoculum is alternative hosts, namely wild grass species that grow in borders alongside barley crops. Rhynchosporium is commonly found on these grasses. However, in 2010 it was proposed that Rhynchosporium found on different hosts is strictly host-specific. The four proposed species within the Rhynchosporium genus are:

R. commune (causes lesions on barley)

R. agropyri (on couch-grass)

R. secalis (on rye / triticale)

R. orthosporum (on cocksfoot).

This PhD project has investigated whether the proposal for the Rhynchosporium species complex, as outlined above, should be accepted. To do this, isolates were collected from different hosts including previously unexamined wild grasses. Further, isolates came from diverse locations: e.g. the UK, France, Romania and Switzerland. Strains from different hosts were compared for similarities / differences in:

Infection biology

Morphology

Genetic structure

Host range

This project has also examined whether Rhynchosporium (all species) possess a cryptic sexual cycle. Rhynchosporium has many signatures of a sexually reproducing pathogen, including high genetic variability and the presence of two mating type alleles in a 1:1 distribution for most populations. Current work is attempting to induce the sexual stage of Rhynchosporium on different media by crossing of genetically characterised isolates of compatible mating type.